U.S. Pat. No. 3,489,198 discloses a method of mounting and removing large-sized pneumatic tires on drop center rims by moving a pair of bead deflectors in opposite senses about the rim flange commencing at a point at which a thrust force is applied partly inward against the tire tread. This patent also discloses apparatus including a platform on which a rim is held horizontal, and side-by-side shafts projecting upward through the periphery of the rim, between the bead to be deflected and the rim, in opposite 180.degree. arcs. Since the bead deflectors were on telescoping arms projecting from non-concentric shafts and would bear against the rim edge, much friction accompanied their movement, limiting the capacity of the machine.
Since that patent was applied for, much larger and wider pneumatic tires have been manufactured for carrying extremely heavy loads, and the tire beads and rim bead seat portions have been standardized. The beads are often so large as not to fit readily adjacent to each other within the drop center portion of a drop center rim. It may be impossible to have both of the tire beads fully within the drop center portion at the same time. After the lower bead of the tire has been deflected over the upper flange of a horizontally-held rim, the lower bead will tend to remain at least in part in the drop center, holding the upper bead above the upper rim flange. Before air pressure is applied within the tire, there is no feasible way to drive a lower tire bead onto its bead seat and fully out of the drop center. Thus the lower bead interferes with mounting the upper bead. This factor, unless overcome, would deter use of drop center rims for these heavy tires with large beads.
These problems of mounting the upper tire bead have been identified:
1. While the lower bead is resting on the wall portion which leads from the drop center to the lower bead seating surface and occupies at least part of the drop center, it holds the upper bead high above the upper flange of the rim, requiring an initial sharp downward deflection to tuck a starting portion of the upper bead beneath the rim flange. Applying such an initial sharp downward force is inconsistent with applying a horizontal or transverse shifting of the tire sidewall, as taught in U.S. Pat. No. 3,489,198.
2. The presence of at least a part of the lower bead in the drop center interferes with the full entry of the upper bead into the drop center, as required for maximum transverse shifting.
These difficulties relate only to mounting the upper bead; when the lower bead enters the drop center nothing there interferes with it; it may be mounted as set forth in my U.S. Pat. No. 3,489,198.